Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $146.39   10.317%   $161.4931   $161.49   $161.50   $161.50  
  Purchase #2 $56.61   4.232%   $59.0057   $59.01   $59.00   $59.00  
  Purchase #3 $134.77   6.448%   $143.46   $143.46   $143.45   $143.50  
  Purchase #4 $243.98   4.469%   $254.8835   $254.88   $254.90   $254.90  
  Purchase #5 $190.80   3.304%   $197.104   $197.10   $197.10   $197.10  
  Purchase #6 $32.36   12.147%   $36.2908   $36.29   $36.30   $36.30  
  Purchase #7 $141.47   4.569%   $147.9338   $147.93   $147.95   $147.90  
  7 purchase totals = $946.38       $1,000.1709   $1,000.16   $1,000.20   $1,000.20